> So i'd argue to not backmerge during the merge window (and i have stopped > doing that myself a few cycles ago, and it clearly helped things) - but in > any case it's certainly no big deal and up to Linus i guess.

What i do instead is that once Linus pulls from me i pull back immediately to test, and if it's fine i base further subsystem patches on that and test the heck out of the combination from that point on.

That's the collective 'point of no looking back' when subsystem people should jump in and help out testing the "final" combination.

But if a subsystem tree backmerges during the merge window any sooner (_before_ Linus pulls), it can cause criss-cross merges (as Linus may not pull or may pull later during which fixes arrive, etc.), creating a less readable history, etc. - which may make integration and problem isolation somewhat harder in the end.

( It's not a big deal in isolation and i dont think Linus actually rejects trees that do the occasional backmerge - but the combination of many small deals can have a bigger effect. )

There are exceptions, such as tricky conflicts that i know to be problematic - in that case i occasionally backmerge. But it's relatively rare - 90%+ of the conflicts are trivial and all-or-nothing affairs (i.e. if you mess it up the kernel wont work very well, so it's immediately noticeable).